Carrier 30H - Manual (Page 10)

Example;
Design setpoint is at 44 F. On a reduction in load,
the capacity of the unit will be reduced to zero
when return water temperature drops to 44 F, and
unit will cycle off.
WARNING: Any alteration of factory settings,
except design setpoint, without Carrier authori­
zation, may void the Carrier
warranty.
DESIGN SETPOINT ADJUSTMENT
When unit is ready for operation, insert small
screwdriver in adjusting slot (Fig. 8) and rotate to
turn dial (dial may also be turned by hand). Rotate
until the design setpoint for the installation appears
directly under the pointer. Insert a thermometer in
the
return chilled water connection and allow the
unit to run thru a cycle. At the instant the last step of
capacity unloads (switch no. J opens), read the tem­
perature. If it is not the same as the dial reading, the
variation can be compensated by shifting the control
point slightly.
('.•\l ' I K ; N : Do not force the dial past the stop.
This could cause loss of the control point and
damage the instrument.
/ ■. '
ADauSTtNS
SLOT.
LEAVING
WATER
TEMP(F)
DESIGN
POINTER
STOP
CALIBRATED «AL
Fig. 8 — Setpoint Adjustment
CYLINDER UNLOADING SYSTEM
Each unloading device is of the cylinder head
bypass type and unloads 2 cylinders when operating
solenoid is energized. Cylinder unloaders are ener­
gized
and de-energized by load switches in the
temperature controller.
Steps under Cylinder Bank Loaded and Cylinder
Bank Unloaded refer to numbered callouts on
Fig. 9 and 10.
Cylinder Bank Loaded (Fig. 9)
1. With solenoid valve not energized, gas bypass
port is closed by solenoid valve stem.
2. Discharge manifold pressure extends thru the
strainer and bleed orifice into solenoid valve
stem chamber and behind bypass piston.
3. Refrigerant pressure overcomes bypass valve
spring pressure and forces piston forward closing
the bypass from the discharge manifold to the
suction manifold.
4. Cylinder bank discharge pressure forces open the
discharge piston check valve. Refrigerant gas
enters the discharge manifold.
As long as the solenoid valve is not energized, the
cylinder bank will continue to operate fully loaded.
,, i
Fig. 9 — Cylinder Bank Loaded
Cylinder Bank Unloaded (Fig. 10)
1. When solenoid valve is energized, gas bypass port
is opened by solenoid valve stem.
2. Discharge manifold pressure extends into sole­
noid valve stem chamber and behind bypass
piston.
3. Open gas bypass port allows pressure to bleed
into suction manifold causing reduction of pres­
sure behind bypass piston.
4. When bypass valve spring pressure overcomes
gas pressure behind piston, the piston moves
back, opening bypass from discharge manifold to
suction manifold.
5. Cylinder discharge pressure on face of check
valve piston is reduced and discharge manifold
pressure closes check valve. The cylinder bank is
now isolated from discharge manifold.
As long as solenoid valve is energized, cylinder
bank will operate fully unloaded.
D ischarge
FlSTON
CHECK VALVE
ASSEMBLY
DISCHARGE
MANIFOLD
f
Fig. 10 — Cylinder Bank Unloaded
1 0